U.S. patent application number 11/231797 was filed with the patent office on 2007-03-22 for anti-ferromagnetically coupled soft underlayer.
This patent application is currently assigned to SEAGATE TECHNOLOGY LLC. Invention is credited to Charles Frederick Brucker, Alexander Yulievich Dobin, Erol Girt.
Application Number | 20070065681 11/231797 |
Document ID | / |
Family ID | 37884541 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070065681 |
Kind Code |
A1 |
Girt; Erol ; et al. |
March 22, 2007 |
Anti-ferromagnetically coupled soft underlayer
Abstract
A magnetic recording medium having a first magnetic layer, a
spacer layer, and a second magnetic layer, in this order, wherein
the spacer layer includes a non-magnetic layer and a thickness of
the spacer layer is selected to establish anti-ferromagnetic
coupling between the first magnetic layer and the second magnetic
layer, and a thickness of both the first and second magnetic layers
are less than a critical thickness for formation of stripe domains
in the magnetic layers is disclosed.
Inventors: |
Girt; Erol; (Berkeley,
CA) ; Brucker; Charles Frederick; (Pleasanton,
CA) ; Dobin; Alexander Yulievich; (Milpitas,
CA) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD
SUITE 300
MCLEAN
VA
22102
US
|
Assignee: |
SEAGATE TECHNOLOGY LLC
Scotts Valley
CA
|
Family ID: |
37884541 |
Appl. No.: |
11/231797 |
Filed: |
September 22, 2005 |
Current U.S.
Class: |
428/828 ;
428/828.1; G9B/5.288 |
Current CPC
Class: |
G11B 5/667 20130101;
G11B 5/66 20130101; G11B 5/653 20130101 |
Class at
Publication: |
428/828 ;
428/828.1 |
International
Class: |
G11B 5/66 20060101
G11B005/66 |
Claims
1. A magnetic recording medium comprising a first magnetic layer, a
spacer layer, and a second magnetic layer, in this order, wherein
the spacer layer comprises a non-magnetic layer and a thickness of
the spacer layer is selected to establish anti-ferromagnetic
coupling between the first magnetic layer and the second magnetic
layer, and a thickness of both the first and second magnetic layers
are less than a critical thickness for formation of a stripe domain
in the magnetic layers.
2. The magnetic recording medium of claim 1, wherein erasure of the
magnetic recording medium is less than about 5%.
3. The magnetic recording medium of claim 1, wherein the critical
thickness of the first and second magnetic layers is in a range of
about 40 to 150 nm.
4. The magnetic recording medium of claim 3, wherein the first and
second magnetic layers comprise a Fe-containing alloy of a material
selected from the group consisting of Co, B, P, Si, C, Zr, Nb, Hf,
Ta, Al, Si, Cu, Ag, Au, Nd, Sm, Tb, Dy, Ho and combinations
thereof.
5. The magnetic recording medium of claim 1, wherein the thickness
of the spacer layer is in a range of about 0.1 to 4 nm.
6. The magnetic recording medium of claim 5, wherein the spacer
layer comprises a material selected from the group consisting of
Ru, Rh, Ir, Cr, Cu, Re, V and combinations thereof.
7. The magnetic recording medium of claim 1, further comprising an
interface layer between the first magnetic layer and the spacer
layer or the second magnetic layer and the spacer layer.
8. The magnetic recording medium of claim 7, wherein a thickness of
the interface layer is in a range of about 0.1 to 10 nm.
9. The magnetic recording medium of claim 1, further comprising
additional magnetic layers and an additional spacer layer, wherein
the additional magnetic layers are ferromagnetically coupled across
the additional spacer layer.
10. The magnetic recording medium of claim 1, further comprising
additional magnetic layers and an additional spacer layer, wherein
the additional magnetic layers are anti-ferromagnetically coupled
across the additional spacer layer.
11. A method of manufacturing a recording medium, comprising
obtaining a substrate, depositing a first magnetic layer,
depositing a spacer layer, and depositing a second magnetic layer,
in this order, wherein the spacer layer comprises a non-magnetic
layer and a thickness of the spacer layer is selected to establish
anti-ferromagnetic coupling between the first magnetic layer and
the second magnetic layer, and a thickness of both the first and
second magnetic layers are less than a critical thickness for
formation of a stripe domain in the magnetic layers.
12. The method of claim 11, wherein erasure of the magnetic
recording medium is less than about 5%.
13. The method of claim 11, wherein the critical thickness of the
first and second magnetic layers is in a range of about 40 to 150
nm.
14. The method of claim 13, wherein the first and second magnetic
layers comprise a Fe-containing alloy of a material selected from
the group consisting of Co, B, P, Si, C, Zr, Nb, Hf, Ta, Al, Si,
Cu, Ag, Au, Nd, Sm, Tb, Dy, Ho and combinations thereof.
15. The method of claim 11, wherein the thickness of the spacer
layer is in a range of about 0.1 to 4 nm.
16. The method of claim 15, wherein the spacer layer comprises a
material selected from the group consisting of Ru, Rh, Ir, Cr, Cu,
Re, V and combinations thereof.
17. The method of claim 11, further comprising depositing an
interface layer between the first magnetic layer and the spacer
layer or the second magnetic layer and the spacer layer.
18. The method of claim 17, wherein a thickness of the interface
layer is in a range of about 0.1 to 10 nm.
19. The magnetic recording medium of claim 1, wherein at least one
of the first and second magnetic layers is amorphous.
20. The magnetic recording medium of claim 1, wherein at least one
of the first and second magnetic layers is crystalline.
Description
FIELD OF INVENTION
[0001] This invention relates to perpendicular recording media,
such as thin film magnetic recording disks having perpendicular
recording, and to a method of manufacturing the media. The
embodiments of the invention have particular applicability to
perpendicular media having an anti-ferromagnetically coupled soft
underlayer.
BACKGROUND
[0002] Perpendicular magnetic recording systems have been developed
for use in computer hard disc drives to provide higher liner
density than longitudinal recording. FIG. 1, obtained from Magnetic
Disk Drive Technology by Kanu G. Ashar, 322 (1997), shows magnetic
bits and transitions in longitudinal and perpendicular recording.
In a longitudinal recording there exists a demagnetization field
between two magnetic bits. These demagnetization fields tend to
separate bits, making transition space between bits, that is,
transition parameter a, large as shown in FIG. 1(a). At very high
bit densities, the limiting parameter may be the length of the
transition region. Perpendicular recording bits do not face each
other, and hence they can be written at closed distances as shown
in FIG. 1(b).
[0003] A typical perpendicular recording head includes a trailing
read/write pole, a leading return or opposing pole magnetically
coupled to the read/write pole, and an electrically conductive
magnetizing coil surrounding the yoke of the write pole as shown in
FIG. 2, Magnetic Disk Drive Technology by Kanu G. Ashar, 323
(1997). Perpendicular recording media may include magnetic media
and an underlayer as shown in FIG. 2. The magnetic media could be a
hard magnetic recording layer with vertically oriented magnetic
domains and the underlayer could be a soft magnetic underlayer to
enhance the recording head fields and provide a flux path from the
trailing write pole to the leading or opposing pole of the writer.
The magnetic flux passes from the write pole tip, through the hard
magnetic recording track, into the soft underlayer (SUL), and
across to the opposing pole. Such perpendicular recording media may
also include a thin interlayer between the hard recording layer and
the soft underlayer to prevent exchange coupling between the hard
and soft layers. The soft underlayer helps also during the read
operation. During the read back process, the soft underlayer
produces the image of magnetic charges in the magnetically hard
layer, effectively increasing the magnetic flux coming from the
medium. This provides a higher playback signal.
[0004] The soft underlayer is located below a recording layer and
forms a mirror image of the recording head. Together with the image
head, there are essentially two heads involved in each recording
event; thus, the net recording field becomes fairly large compared
to the field generated with a longitudinal head. Magnetic flux
flows from head through the SUL to return pole crossing twice
through the recording layer. The return pole is generally much
wider than the writing pole in order to dilute the magnetic flux
intensity flow back through the recording layer. In spite of this,
it is sometimes found that writing also occurs at the return pole,
with the consequence that data can be partially erased not only on
the track being recorded, but also on an adjacent track resulting
in unintentional erasure of data stored in the recording layer. The
quality of the image, and therefore the effectiveness of the soft
underlayer, and erasure of data both depend on the permeability of
the soft underlayer. Thus, there is a need for a perpendicular
recording medium having a soft underlayer that forms a good mirror
image of the recording head without erasure of data in the
recording layer.
SUMMARY OF THE INVENTION
[0005] The embodiments of the invention are directed to a
perpendicular recording medium having a SUL structure having an
anti-ferromagnetically coupled SUL design. This design allows
adjusting the permeability of the SUL independent of the SUL
saturation magnetization to substantially prevent erasure of
recording layer without compromising writability.
[0006] As will be realized, this invention is capable of other and
different embodiments, and its details are capable of modifications
in various obvious respects, all without departing from this
invention. Accordingly, the drawings and description are to be
regarded as illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows (a) longitudinal and (b) perpendicular
recording bits.
[0008] FIG. 2 perpendicular pole head with magnetic media and
underlayer.
[0009] FIG. 3 is a schematic of an embodiment of a perpendicular
recording medium of this invention with a film structure having a
substrate, an adhesion layer, an AFC soft underlayer, a
non-magnetic interlayer, a recording layer, and a carbon layer.
[0010] FIGS. 4(a)-(d) show different embodiments of AFC SUL
structures with FML--ferromagnetic layer, SL--spacer layer,
IFL--interface layer, Ru--ruthenium layer.
[0011] FIG. 5 shows RKKY coupling between FeCoB layers a function
of Ru thickness an embodiment of this invention.
[0012] FIG. 6 shows that the recording performance of media of an
embodiment of this invention does not deteriorate if a Ru spacer
layer thickness is below 1.1 nm.
[0013] FIG. 7 shows that overwrite in media of an embodiment of
this invention decreases if anti-ferromagnetic coupling between
FeCoB layer increases.
[0014] FIG. 8 shows that erasure of media of an embodiment of this
invention improves significantly if anti-ferromagnetic coupling
between FeCoB layer increases.
[0015] FIG. 9 shows critical thickness without stripe domains of
the soft underlayer as function of a Ru layer spacer layer in an
embodiment of this invention.
DETAILED DESCRIPTION
[0016] A perpendicular recording medium could have ferromagnetic
and antiferromagnetic coupling in a soft magnetic underlayer of the
perpendicular recording medium. The embodiments of the invention
provide an antiferromagnetic coupling in a soft magnetic underlayer
of the perpendicular recording medium. The embodiments of the
invention are particularly suitable for use with a magnetic disc
storage system with a recording head having a head capable of
performing read and/or write operations. Ferromagnetic coupling
generally refers to indirect coupling between ferromagnetic layers
or multilayer structures such that adjacent ferromagnetic layers or
multilayer structures have magnetizations that point in generally
the same directions. Antiferromagnetic coupling generally refers to
the coupling between ferromagnetic layers or multilayer structures
such that adjacent ferromagnetic layers or multilayer structures
have magnetizations that point in generally opposite
directions.
[0017] The AF coupling was evaluated by measuring J.sub.ex, the
exchange energy density of the system, which represents the
strength of antiferromagnetic coupling between two magnetic layers.
In the embodiments of this invention, there is antiferromagnetic
coupling between ferromagnetic layers or multilayer structures such
that adjacent ferromagnetic layers or multilayer structures when
the value of J.sub.ex between ferromagnetic layers or multilayer
structures such that adjacent ferromagnetic layers or a multilayer
structure is greater than zero erg/cm.sup.2.
[0018] The preferred embodiment of the perpendicular medium of this
invention allows the SUL permeability to be controlled independent
of the SUL saturation magnetization such that erasure of data in
the magnetic layer is substantially prevented without compromising
writability. If one changes the strength of RKKY interaction
between magnetic layers in SUL one automatically changes the
permeability of SUL (larger coupling, lower permeability). The
reduction in permeability would decrease writability and at the
same time reduce erasure. So there is an optimum point for which
erasure can be significantly reduced without decreasing writability
significantly. So changing permeability is one way to optimize
media performance by changing erasure and writability.
[0019] The embodiments of the invention provide magnetic recording
media suitable for high a real recording density exhibiting high
SMNR. The embodiments of the invention achieve such technological
advantages by forming a soft underlayer. A "soft magnetic material"
is a material that is easily magnetized and demagnetized. As
compared to a soft magnetic material, a "hard magnetic" material is
one that neither magnetizes nor demagnetizes easily.
[0020] The underlayer is "soft" because it is made up of a soft
magnetic material, which is defined above, and it is called an
"underlayer" because it resides under a recording layer. In a
preferred embodiment, the soft layer is amorphous. The term
"amorphous" means that the material of the underlayer exhibits no
predominant sharp peak in an X-ray diffraction pattern as compared
to background noise. The "amorphous soft underlayer" of the
embodiments of the invention encompasses nanocrystallites in
amorphous phase or any other form of a material so long the
material exhibits no predominant sharp peak in an X-ray diffraction
pattern as compared to background noise.
[0021] When soft underlayers are fabricated by magnetron sputtering
on disk substrates, there are several components competing to
determine the net anisotropy of the underlayers: effect of
magnetron field, magnetostriction of film and stress originated
from substrate shape, etc. The first and second soft magnetic
underlayers can be fabricated as single layers or a multilayer.
[0022] The soft magnetic layer could be deposited from targets
manufactured by a gas atomized alloyed powder process (AP) or by a
molten material casting into a mold at a temperature between 1200
to 1550.degree. C., and solidifying into an ingot. The ingot could
then pre-heated to a temperature between 850 and 1200.degree. C. in
an annealing furnace suitable for rolling to desired thickness for
final machining to precise target size.
[0023] A seedlayer is a layer lying in between the substrate and
the underlayer. Proper seedlayer can also control anisotropy of the
soft underlayer by promoting microstructure that exhibit either
short-range ordering under the influence of magnetron field or
different magnetostriction. A seedlayer could also alter local
stresses in the soft underlayer.
[0024] Preferably, in the underlayer of the perpendicular recording
medium of the embodiments of the invention, an easy axis of
magnetization is directed in a direction substantially transverse
to a traveling direction of the magnetic head. This means that the
easy axis of magnetization is directed more toward a direction
transverse to the traveling direction of the read-write head than
toward the traveling direction. Also, preferably, the underlayer of
the perpendicular recording medium has a substantially radial or
transverse anisotropy, which means that the domains of the soft
magnetic material of the underlayer are directed more toward a
direction transverse to the traveling direction of the read-write
head than toward the traveling direction. In one embodiment, the
direction transverse to the traveling direction of the read-write
head is the direction perpendicular to the plane of the substrate
of the recording medium.
[0025] In accordance with embodiments of this invention, the
substrates that may be used in the embodiments of the invention
include glass, glass-ceramic, NiP/aluminum, metal alloys,
plastic/polymer material, ceramic, glass-polymer, composite
materials or other non-magnetic materials. Glass-ceramic materials
do not normally exhibit a crystalline surface. Glasses and
glass-ceramics generally exhibit high resistance to shocks.
[0026] A preferred embodiment of this invention is a perpendicular
recording medium comprising at least two amorphous soft underlayers
with a spacer layer between the underlayers and a recording layer.
The amorphous soft underlayer should preferably be made of soft
magnetic materials and the recording layer should preferably be
made of hard magnetic materials. The amorphous soft underlayer is
relatively thick compared to other layers. Any layer between the
amorphous soft underlayer and the recording layer is called an
interlayer or an intermediate layer. An interlayer can be made of
more than one layer of non-magnetic materials. The purpose of the
interlayer is to prevent an interaction between the amorphous soft
magnetic underlayer and recording layer. An interlayer could also
promote the desired properties of the recording layer. Longitudinal
recording media do not have an amorphous soft magnetic underlayer.
Therefore, the layers named as "underlayer," "seed layer,"
"sub-seed layer," or "buffer layer" of longitudinal media are
somewhat equivalent to the intermediate layer(s) of perpendicular
media.
[0027] The underlayer and magnetic recording layer could be
sequentially sputter deposited on the substrate, typically by
magnetron sputtering, in an inert gas atmosphere. A carbon overcoat
could be typically deposited in argon with nitrogen, hydrogen or
ethylene. Conventional lubricant topcoats are typically less than
about 20 .ANG. thick.
[0028] A seedlayer, which could be optionally added as a layer
lying in between the substrate and the soft underlayer, can often
control anisotropy of the soft underlayer by promoting
microstructure that exhibit either short-range ordering under the
influence of magnetron field or different magnetostriction. A
seedlayer could also alter local stresses in the soft
underlayer.
[0029] Amorphous soft underlayers could produce smoother surfaces
as compared to polycrystalline underlayers. Therefore, amorphous
soft underlayer could be one way of reducing the roughness of the
magnetic recording media for high-density perpendicular magnetic
recording. The amorphous soft underlayer materials include a
Cr-doped Fe-alloy-containing underlayer, wherein the Fe-alloy could
be CoFeZr, CoFeTa, FeCoZrB and FeCoB.
[0030] Another advantage of amorphous materials as soft underlayer
materials is the lack of long-range order in the amorphous
material. Without a long-range order, amorphous alloys have
substantially no magnetocrystalline anisotropy. The use of
amorphous soft underlayer could be one way of reducing noise caused
by ripple domains and surface roughness. The surface roughness of
the amorphous soft underlayer is preferably below 1 nm, more
preferably below 0.5 nm, and most preferably below 0.3 nm.
[0031] In accordance with the embodiments of the invention, the
test methods for determining different parameters are as follows.
If a particular test method has not been explicitly stated below to
determine a parameter, then a conventional method used by persons
of ordinary skill in this art could be used to determine that
parameter.
[0032] Writability: In the embodiments of this invention, the
preferred range of writability includes high values.
[0033] Remanent magnetization: In the embodiments of this
invention, the preferred range of saturation magnetization is 0.3
to 1 memu/cm.sup.2, more preferably, 0.4 to 0.7 memu/cm.sup.2.
[0034] Magnetostriction, .lamda..sub.s: In the embodiments of this
invention, the preferred range of .lamda..sub.s is depends on the
SUL composition. For example, .lamda..sub.s (x10.sup.-5) could in
the range about 5.2 to 4.4 when boron content increases from about
8 to 12 at. %.
[0035] Stress, .sigma.: In the embodiments of this invention, the
preferred range of .sigma. depends on sputtering conditions. For
example, .sigma. can vary in the range from about -400 to about 800
MPa when the sputtering pressure increases from about 2 to 12
mTorr, and then decrease to about 400 MPa when the sputtering
pressure is further increased to about 15 mTorr. See C. L. Platt,
M. K. Minor, T. J. Klemmer, "Magnetic and structural properties of
FeCoB thin films", IEEE Trans. Magn., vol. 37, pp. 2302-2304, July
2001.
[0036] Stripe domain: They introduce noise so SUL should be without
stripe domains. Strip domains are stripe structures in an otherwise
optically smooth film of SUL. Strip domain is measured by using
Magnetic Force Microscopy (MFM) with soft magnetic tips magnetized
perpendicular to the sample plane.
[0037] J.sub.ex: Exchange energy density--describes strength of
RKKY interaction. In this invention, the preferred value of
J.sub.ex is greater than zero erg/cm.sup.2, more preferably greater
than 2 erg/cm.sup.2. More preferably between 0 and 0.5
erg/cm.sup.2. Even more preferably between 0 and 0.2
erg/cm.sup.2.
[0038] Signal to media noise ratio (SMNR): In the embodiments of
this invention, the preferred range of SMNR includes high
values.
[0039] Reverse overwrite (rev OW): In the embodiments of this
invention, the preferred range of rev OW includes high values.
[0040] Erasure: In the embodiments of this invention, the preferred
range of erasure includes low values.
[0041] A preferred embodiment of a perpendicular recording medium
of this invention is shown in FIG. 3. The layer structure of the
preferred embodiment is as follows: Substrate, adhesion layer (1),
anti-ferromagnetically coupled (AFC) soft underlayer (2),
non-magnetic interlayer/s (3), recording layer/s (4), and carbon
layer (5). Preferably, the AFC soft underlayer comprises a first
soft underlayer, a spacer layer, and a second soft underlayer.
Protective carbon layer 5 typically covers the magnetic recording
layer 4.
[0042] The adhesion layer could comprise Cr, CrTi, Ti, and NiNb
among other adhesion promoting materials. The thickness of adhesion
layer 1 is in the range of about 0.5 nm, preferably in the range of
about 10 nm.
[0043] The anti-ferromagnetically coupled soft underlayer (AFC SUL)
comprises least two ferromagnetic layers (FML) that are
anti-ferromagnetically coupled across a non-magnetic spacer layer
(SL).
[0044] The AFC SUL could have several different possible structures
as follows: [0045] (1) FML/SL/FML (thickness of SL adjusted to
establish anti-ferromagnetic coupling between FML); [0046] (2)
FML/IFL/SL/FML or FML/SL/IFL/FML or FML/IFL/SL/IFL/FML
(IFL--interface layer used to enhance anti-ferromagnetic coupling
between FML) (thickness of SL adjusted to establish
anti-ferromagnetic coupling between FML); [0047] (3)
FML/IFL/nx[SL/IFL/FML] (n=2 to 20) (thickness of SL adjusted to
establish anti-ferromagnetic coupling between FML) (IFL may or may
not be present); [0048] (4) FMLI/IFL/nx[SL.sub.i/IFL/FML.sub.i+1]
(n=2 to 20) (example:
FML.sub.1/SL.sub.1/FML.sub.2/SL.sub.2/FML.sub.3/SL.sub.3/FML.su-
b.4. . . ) (thickness of SL.sub.i can vary from 0 to 2.5 to
establish all ranges of coupling between FML.sub.i and at least one
SL.sub.i is adjusted to establish anti-ferromagnetic coupling
between FML.sub.i and FML.sub.i+1) (IFL may or may not be present);
and [0049] (5) FML.sub.1/IFL/nx[SL.sub.i/IFL/FML.sub.i+1](n=2 to
20) (example:
FML.sub.1/SL.sub.1/FML.sub.2/SL.sub.2/FML.sub.3/SL.sub.3/FML.sub.4.
. . ) (thickness of SL.sub.i is adjusted so that anti-ferromagnetic
coupling strength between FML.sub.i and FML.sub.i+i, J.sub.ex(i),
varies across AFC SUL from weak near the layer 4 to strong near the
substrate) (IFL may or may not be present). Some of the embodiments
of the structures of AFC SUL are shown in FIGS. 4(a)-(d).
[0050] The ferromagnetic soft underlayer could comprises an alloy
material selected from the group consisting of Fe with one or more
elements selected from Co, B, P, Si, C, Zr, Nb, Hf, Ta, Al, Si, Cu,
Ag, Au. The thickness of the first or second soft magnetic
underlayer (FML) is preferably in the range of 5-400 nm, more
preferably, in the range of about 40-150 nm.
[0051] Note that large magnetostriction, .lamda..sub.S, and stress,
.sigma., in FML can generate perpendicular anisotropy (because
K.sub.u=3/2.lamda..sub.S.sigma., where Ku refers to uniaxial
anisotropy) that can induce formation of stripe domains if
thickness of FML exceeds some critical value. During the course of
this invention, it was found that anti-ferromagnetic coupling
between FML can suppress the formation of stripe domains in FML.
Moreover, it was observed that the critical thickness of FML, i.e.,
the thickness at which stripe domains are formed in FML, increases
if the strength of anti-ferromagnetic coupling increases.
[0052] The spacer layer could comprise nearly any non-magnetic
composition, but may include Ru, Rh, Ir, Cr, Cu, Re, V and their
alloys. The thickness of the spacer layer is in the range of about
0.1-2.5 nm, preferably in the range of about 0.3-1 nm.
[0053] The interface layer (IFL) could comprise Co, Fe, B, P, Si,
C, Zr, Nb, Hf, Ta, Al, Si, Cu, Ag, Au and their alloys.
Magnetization saturation of this layer should preferably be at
least 800 emu/cm.sup.3. The thickness of interface layer is in the
range of about 0.1-10 nm, preferably in the range of about 0.5-2
nm.
[0054] Preferably, the interlayer should be such that it sets a
growth of recording layer. For example, this layer may include one
or more layers with fcc or/and hcp crystallographic structure and
have a following composition: one or more elements selected from
Ru, Re, Ir, Cu, Ag, Au, Zr, Hf, Pr, Pd and Ti with a minor amounts
of bcc-structured elements selected from the group consisting of W,
Mo, Ta, Nb, Cr, and V. The thickness of interlayer layer is in the
range of about 0.2 nm to 40 nm, preferably in the range of about
4-12 nm.
[0055] The recording layer could be of one or more magnetic layers.
The recording layer could be grown in controlled atmosphere, in
general Ar or combination of Ar and O.sub.2. This layer may be
grown at low temperatures, below 400 K (in general this temperature
range is used for magnetic layers that are sputtered in combination
of Ar and O.sub.2 atmosphere), or may be grown at elevated
temperatures, in general above 420 K and below 600 K. The recording
layer may include Co with one or more added elements selected from
B, C, Si, Ti, V, Cr, Mn, Fe, Ni, Cu, Ge, Zr, Nb, Mo, Ru, Rh, Pd,
Ag, Hf, Ta, W, Re, Ir, Pt, Au, B, and C. This layer may also
include at least one oxide material selected from group consisting
of B, Mg, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ge, Y, Zr, Nb, Mo, Ru,
Rh, Pd, Ag, Hf, Ta, W, Re, Ir and Pt oxides. For example,
CoCrPt+SiO.sub.2 The thickness of magnetic layer 4 is in the range
of about 4 to 30 nm, preferably in the range of about 8 to 20
nm.
[0056] Optionally, amorphous layer (AmL) may be present, for
example, if layer 2 is not amorphous. This layer can include a
magnetic or non-magnetic material having a composition for which
these materials are amorphous, for example: FeCoB, CZN,
Ti.sub..delta.Cr.sub.100-.delta., Ta.sub..delta.Cr.sub.100-.delta.
(30<.delta.<60), NiTa, NiNb, NiP, and CrZr. The thickness of
the optional amorphous layer is in the range of about 0-10 nm,
preferably, about 0.2-20 nm.
[0057] The advantageous characteristics attainable by the
embodiments of the invention are illustrated in the following
examples.
EXAMPLES
[0058] All samples described in this disclosure were fabricated
with DC magnetron sputtering except carbon films were made with AC
magnetron sputtering.
[0059] The applicants investigated perpendicular granular media
with AFC SUL structure: FeCoB[57 nm]/Ru/FeCoB[57 nm]/Cu/IL/Mag,
where Ru thickness was varied from 0 to 2.2 nm and found that the
RKKY coupling between FeCoB layers was a function of Ru thickness
as shown in FIG. 5. FIG. 5 describes how J.sub.ex varies with Ru
thickness. So anti-ferromagnetic coupling can be achieved from
0.3.+-.0.2 to 0.9.+-.0.2 nm and from 1.7.+-.0.2 to about 2.6.+-.0.2
nm for used sputtering conditions. However, if the sputtering
conditions are changed, for example Ar sputtering pressure is
increased the interface roughness changes leading to different Ru
thickness values for which ferromagnetic layers in SUL are
anti-ferromagnetically coupled. For this reason I would claim any
Ru thickness for which ferromagnetic layers in SUL are
anti-ferromagnetically coupled.
[0060] Origin of RKKY interaction is polarization of conducting
electrons induced by localized spin. Atoms of magnetic layers at
the interface with non-magnetic layer (localized spins on the
interface) polarize conducting electrons in non-magnetic layer.
Depending on the thickness of non-magnetic layer, exchange
interaction can vary from ferromagnetic to anti-ferromagnetic as
shown in FIG. 5. Exchange is largely a nearest-neighbor phenomenon
that occurs across distances typical of the distance between atoms
in a solid (a few angstroms). If there is one atomic spacer layer
of one material between two magnetic layers, then that may be
enough (though a thicker spacer layer could also by used) to
destroy or further stabilize the exchange between the two magnetic
layers separated by the spacer layer.
[0061] FIG. 6 is a plot of SMNR versus Ru layer thickness, showing
that the recording performance of the media does not deteriorate if
Ru thickness below 1.1 nm.
[0062] FIG. 7 is a plot of overwrite as a function write current
SUL having different AFC, showing that overwrite in the media
decrease when the anti-ferromagnetic coupling between the SUL
layers of FeCoB increases.
[0063] FIG. 8 is a plot of erasure as a function of
anti-ferromagnetic coupling defined in terms of J.sub.ex
(erg/cm.sup.2), showing that erasure of the media improves
significantly if anti-ferromagnetic coupling between the soft
underlayers of FeCoB layer increases.
[0064] Thus, this invention demonstrates that coupling between
FeCoB layer is an important parameter for preventing erasure, and
the presence of interface layers may be important for adjusting
optimum recording performance.
[0065] The applicants further investigated perpendicular granular
media with AFC SUL structure: FeCoB[y]/Ru/FeCoB[y]/Cu/IL/Mag, where
Ru thickness x was varied from 0 to 0.8 nm and FeCoB thickness
varied from 56 to 130 nm. If the thickness of single FeCoB layer
exceeded 125 nm, the applicants observed stripe domains in FeCoB
layer. The thickness at which stripe domains are formed is called a
critical thickness for the formation of stripe domain. When the
applicants inserted about 0.85 nm thick Ru layer in-between two
FeCoB layers the critical thickness of each FeCoB layer was 70 nm.
Note that if the Ru thickness was about 0.85 nm, RKKY coupling
between FeCoB was negligible. On the other hand, when applicants
inserted about 0.5 nm thick Ru layer in-between two FeCoB layers
the critical thickness of each FeCoB layer was 115 nm. This
increase in critical thickness was due to a large
anti-ferromagnetic coupling between FeCoB layers across 0.5 nm Ru
spacer layer. Thus, applicants demonstrated that AFC SUL can be
used to increase total SUL thickness with anti-ferromagnetic
coupling without formation of stripe domains decreasing the Ru
layer thickness as shown in FIG. 9.
[0066] In FIG. 10, applicants have plotted the critical SUL
thickness without stripe domain as a function of AFC defined in
terms of J.sub.ex. FIG. 10 shows that the critical SUL thickness is
initially linear with J.sub.ex but then levels off for large
J.sub.ex.
[0067] This application discloses several numerical range
limitations that support any range within the disclosed numerical
ranges even though a precise range limitation is not stated
verbatim in the specification because this invention can be
practiced throughout the disclosed numerical ranges. Finally, the
entire disclosure of the patents and publications referred in this
application are hereby incorporated herein in entirety by
reference.
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